You can now restrict results to an arbitrary date range by putting the range in {} after your search term(s). For example,

kalter {1903-1923}

will restrict results to sources dated 1903-1923 and satisfying any other restrictions you have imposed (e.g., only within Poland).

This feature was requested by Philip Trauring. If you would like to see other functionality added, post your requests in the Suggestions forum. Adding new sources is generally a higher priority than adding features, with exceptions being features that are very easy to add, like this one.